1. Field of the Invention
The present invention relates to a method and apparatus for pre-processing of semiconductor substrate surface analysis, and more specifically to a method and apparatus for pre-processing for the purpose of analyzing contaminating matter on the surface of a semiconductor substrate.
2. Description of Related Art
In the electronics industry in the past, as devices have become smaller, wafer contamination attributed to materials and impurities generated during necessary operation of processes, and particularly metallic wafer contamination is a problem in terms of causing excessive leakage currents, and deterioration of junction breakdown voltage and oxide film breakdown voltage.
Therefore, for the purpose of achieving higher device reliability and improving production yield, it is necessary to reduce metallic wafer contamination, by achieving high material purity and reducing process contamination. Thus, it is essential to gain a quantitative understanding of the contamination level in manufacturing processes.
In the past, it was said to be necessary to reduce the line contamination level to below 1.times.10.sup.10 atoms/cm.sup.2, and the metallic contamination evaluation technology to analyze this has required a sensitivity of 10.sup.9 atoms/cm.sup.2 or more.
In this metallic contamination impurity analysis method for the surface of a semiconductor silicon substrate, chemical analysis is generally used, such as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 2-28533, which discloses a hydrofluoric acid VPD-AAS (vapor phase decomposition-atomic absorption spectrometry) method and a hydrofluoric acid VDP-ICP-MS (VDP-ICP-MS: vapor phase decomposition-inductively coupled plasma-mass spectrometry) method.
The pre-processing VPD method which is used, as shown in FIG. 7, is that of heating a hydrofluoric acid solution 15 that is supported in a groove 13 inside a hermetically sealed chamber 10 in which semiconductor wafers are resting on a wafer support stand 11, so that the generated hydrofluoric acid vapor decomposes the native oxide film, an oxide film, and a nitride film and the like on the semiconductor substrate.
Additionally, as shown in FIG. 8(A), according to another example disclosed in the above-noted patent publication, a drop 17 of hydrofluoric acid solution is placed on top of a semiconductor substrate 14 which rests on a wafer support stand 11, the wafer support stand 11, as shown in FIG. 8(B) and FIG. 8(C) being undulated up and down so that the drop 17 of the hydrofluoric acid solution is caused to describe a path as shown in FIG. 8(D) and FIG. 8(F) along the surface of the semiconductor substrate 14, so that this acts as a collecting fluid that collects residual metallic impurities therefrom, the collected collecting fluid in this method being measured by AAS or ICP-MS or the like, thereby enabling analysis that is more sensitive than physical analysis methods such as SIMS (secondary ion mass spectrometry) and TXRF (total reflection X-ray fluorescence).
Additionally, in recent years, as disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 2-229428, and as shown in FIG. 9(A) and FIG. 9(B), a pre-processing apparatus has been developed that automates the VPD processing.
FIG. 9 shows a treatment liquid collecting apparatus 10 which comprises a vapor phase decomposition system in which a semiconductor substrate 12, which rests on a carrier 5 provided within a container 2 is decomposed by hydrofluoric acid vapor 4 or the like, a semiconductor substrate transport apparatus 7, and an apparatus 9 which supports a semiconductor substrate 12 on a semiconductor substrate support apparatus 6 and which, by means of a dripping means 8, causes a liquid 17 that is supported by a liquid support part 18 to come into contact with the surface of the semiconductor substrate 12, and scans this, after which it collects the drop by the drop collecting means 9, having a plurality of liquid collecting portions 19.
Of the above-described chemical analysis methods of the past, however, with the VPD method such as shown in FIG. 7 and FIG. 8, which is performed manually by a worker, because it is necessary to perform a scan of the entire surface of the substrate with approximately several hundreds (100) .mu.l of the collecting liquid, the work of scanning the collecting liquid requires that the worker be highly skilled.
In particular in this method, it is difficult to collect impurities around the periphery of the substrate, collecting non-uniformity occurs, and the collecting rate varies between substrates. This presents a problem in performing quantitative analysis.
As the diameters of substrates in the semiconductor industry grow, the larger the substrate size becomes, the larger is the variation in collecting rate, and the larger the collecting time, which leads to atmospheric contamination.
For this reason, although an automatic pre-processing machine has been developed in recent years, several hours are required for substrate surface analysis using hydrofluoric acid vapor, and approximately 10 minutes must be spent on collecting in the case of each 8-inch substrate. As a result of the time required and the fact that it is impossible to scan the entire substrate surface to its periphery with the collecting liquid, this process causes problems of collecting rate and measurement error.
In recent years, because various types of VPD processing collecting decomposition/collecting liquid have come into use, there are various problems, such as unsafe collecting liquids that generate gases and collecting liquids that are hydrophilic on a silicon substrate and therefore difficult to collect.
The present invention can solve these problems.
With regard to substrate surface analysis as in the present invention because of the need to perform quantitative analysis, it is necessary to collect almost 100% of impurities from the surface of a substrate and to collect precisely all of the decomposition/collecting fluid, there has been delay in automating in this field.
An object of the present invention is to provide a pre-processing method for semiconductor substrate analysis which improves on the problems as described above in the prior art, and which uses a simple apparatus to provide highly accurate analysis data by a simply performed analysis.